In the present research project the influence of protein Kinases C and A (cAMP dependent protein kinase) on junctional conductance of isolated rat heart cell pairs will be investigated. Activators of pKC, such as vasopressin, phorbol ester, diacylglycerol, oleoyl-2-acetylglycerol, as well as inhibitors of the kinase (pseudosubstrate or staurosporine) will be used. The influence of PKA on junctional conductance will be further investigated by dialyzing the catalytic subunit of PKA or the protein kinase inhibitors into the cells or adding isoproterenol and forskolyn to the bath. Moreover, the role of G proteins on junctional conductance will be investigated by administering GTP, GDP-B-S and other compounds inside the cells. The interactions between PKA and PKC on the control of junctional conductance will be also investigated. These studies will provide new and valuable knowledge of the physiological and pathological processes involved in the regulation of cell communication in heart.